Many mobile phones on the market today provide phone functionality and also have a built in camera with flash capability in order to take higher quality photos. These phones require circuitry that enables audio functionality for the phone and the flash capability. Audio functionality for a mobile phone is not just limited to the phone functionality but can also include the audio functionality for playing music, games, and videos and running applications and programs.
The camera flashes on mobile phones use light emitting diode (LED) flash drivers to enable flash capability. The majority of these flashes for mobile phones are enabled through a boosted LED flash driver (e.g., having a boost converter). The boost converter is used for powering the LED driver and works to provide a constant current source. The output voltage of the boost converter changes with the forward voltage drop of the LED flash driver because the LED flash driver needs a constant current with a threshold forward voltage applied in order to enable it. The LED flash driver will require a certain power to operate as the battery voltage decreases over time to maintain flash capability, and therefore a boost converter is required. The typical forward voltage drop of the LED flash to enable the LED flash drivers is between 2.6 Volts and 3.8 Volts, and the boost voltage will vary according to the typical forward voltage drop. FIG. 1 shows a forward current versus forward voltage plot diagram for an exemplary LED flash driver in accordance with the prior art that is disclosed in Phillips Lumileds Lighting Company Technical Datasheet DS49 for LUXEON Flash dated October 2006. Generally, the flash driver uses a boost converter that works as a constant current source wherein the flash driver is enabled using hardware pins and configurable via an I2C interface. Such an exemplary LED flash driver is disclosed in Analogic Tech Product Datasheet AAT 1271 for 1.5 A Step-Up Current Regulator for Flash LED dated April 2009.
Also, mobile phones on the market today use a boosted audio amplifier for a more efficient system and for higher and louder audio quality. A boosted audio amplifier comprises a boost converter powering an audio amplifier. By boosting the audio amplifier, the sound output of the amplifier will be increased and louder. In addition, by boosting the voltage to a higher voltage level, the sound output will no longer be clipped by the battery voltage threshold because the audio amplifier is not limited to the voltage supplied by the battery.
Different types of audio amplifiers exist. Such types of amplifiers include but are not limited to Class D, H, A, B, and A-B amplifiers. A boosted class-D amplifier can deliver a higher output power independent of the battery voltage because the boost can guarantee constant deliverance of power into the audio amplifier. When a boost converter is used for powering a class-D amplifier, the boost converter works to provide a constant voltage source to the audio amplifier. In another case, a class-H scheme is implemented to maximize the boost converter efficiency by varying the boost output voltage at a certain signal level. At each respective signal level, the boost converter works to provide a corresponding constant voltage source. One disadvantage of the powering scheme for a boosted Class-D amplifier is that the overall system cost and size increase due to the requirements of additional components related to operating the boost converter with the audio amplifier.
Since both the LED flash driver and the audio amplifier require a similar or same type of boost converter, there is a desire and need for both the LED flash driver and audio amplifier to be supplied by a single boost converter.
FIG. 2 depicts an exemplary block diagram of an LED flash driver and audio amplifier power supply in accordance with the prior art in which a single boost converter is used to simultaneously drive both the LED flash driver and audio amplifier power supply. Such an exemplary circuit implementation is disclosed in Texas Instruments Datasheet for TPS61300, TPS61301, TPS61305 entitled “1.5 A/4.1 A Multiple LED Camera Flash Driver with I2CTM Compatible Interface” dated June 2009 and revised September 2010. Referring to FIG. 2, a constant DC voltage supply 102 is coupled to a capacitor 104 and an inductor 106. Moreover, the inductor 106 is coupled to an integrated circuit (“IC”) 108 that comprises a single boosted LED driver and controller. The boosted LED flash driver IC 108 drives the LED flash light using another capacitor 110 and diodes 112,114. The LED flash driver IC 108 also drives an audio amplifier 124. The audio amplifier 124 comprises a Class-D amplifier 120, two audio inputs 116,118 and a speaker system 122 that outputs an audio signal. Control of LED flash driver IC 108 and audio amplifier 124 is provided at the board level. Such control at the board level can be provided through system software that uses a General Purpose Input/Output (GPIO) port of the LED flash driver IC 108, or an I2C interface. Such control may involve the exclusive operation of either the LED flash driver IC 108 or audio amplifier 124, or operating the LED flash driver IC 108 and the audio amplifier 124 simultaneously. When operating simultaneously, the control includes reducing the gain of the audio amplifier 124. Since the audio amplifier 124 is external to the controller in LED flash driver IC 108, the audio signal level is not monitored before the LED flash is turned on. Thus, the gain amount of the audio signal that needs to be attenuated is hard to determine, and in most cases, due to the high crest factor of music contents, a need to reduce audio gain may not even exist. Thus, the controller for the LED flash driver 108 is limited to being used to control the audio amplifier 124. Therefore, it is desirable to provide a way to control both the LED flash driver and the audio amplifier by using a controller that is on a single integrated circuit.